Mechanical stability of Ca65Mg15Zn20 bulk metallic glass during deformation in the supercooled liquid region

Ca65Mg15Zn20 bulk metallic glass (BMG) samples of dimensions 3.2 mm x 7 nun x 125 mm were prepared using a low-pressure die casting technique. These samples were ground to produce tensile test pieces in compliance with ASTM E8-04. This work is the first reported study of the tensile behaviour of Ca65Mg15Zn20 BMG in the supercooled liquid region (105-120 degrees C). Two deformation conditions were used for testing: (i) constant strain rate testing from 10(-3) to 10(-4) s(-1) and (ii) constant load testing using loads of 20-50 N applied to a tensile sample during heating at a constant rate of 5 degrees C s(-1). The maximum elongation to failure in the BMG was in excess of 850% for constant load testing although, under isothermal testing conditions, most samples failed after similar to 200% elongation. It is concluded that large superplastic elongations (>500%) during isothermal tensile straining is difficult in this alloy due to the onset of crystallization. (C) 2007 Elsevier B.V. All rights reserved.